1. Field of the Invention
The invention relates to a method of selecting a white color temperature of display information to be displayed on a color display device. The invention further relates to a computer programmed for selecting a white color temperature of display information, and to a system and a monitor for selecting a white color temperature of display information.
2. Description of the Related Art
It is known from the trichromatic theory of color vision, that it is possible to generate various colors by mixing three primary colors in various amounts. The various colors can be shown in a color triangle of which the vertices are the primary colors. Often, this color triangle is represented in the well-known chromaticity diagram. The chromaticity diagram shows various monochromatic lights of the spectrum and certain other points as given by their values x and y. The ordinate is the fractional amount of the y primary and the abscissa is the fractional amount of the x primary in any color designated by a point on the diagram. No provision on the diagram is necessary for the third primary z, since it is always true that x+y+z=1 and, consequently, the chromaticity is uniquely determined by x and y. The so-called white point on the diagram is the result of equal amounts of x, y, and z.
Philips Electronics makes a commercially available 17-inch monitor, known as the Brilliance 107, which is supplied together with customax software.
The monitor comprises a video-processing circuit which comprises three controllable amplifiers for amplifying the RGB video signals supplied by a computer with a desired amplification factor. The amplified video signals are supplied as video drive signals to a color display device of the monitor to display the display information. As the hues of colors displayed are determined by ratios of values of the video drive signals, it is possible to alter the hue by correcting the amplification factors of the controlled amplifiers with a correction ratio.
After the customax software has been installed on a PC connected to the monitor, it is possible to open a window wherein a color triangle is displayed. The user can point, with a mouse connected to the computer, to any color in the color triangle. When the customer activates a mouse button, the color pointed to will be selected as the white color of the monitor. The computer sends information to the monitor determining the correction ratio to be applied on the amplification factors of the controllable amplifiers to obtain corrected values of the video drive signals so that white is displayed as the color pointed to. The same correction ratio will be used for all other colors too. In this way, the user is able to select a white color of the display which is in accordance with his personal liking. If the user selects a bluish white, the picture will have a cool appearance, if the user selects a reddish white, the picture will have a warm appearance. It is a drawback of this white color adjustment that it is difficult to select a white or near-white color in the color triangle. This often results in a poor representation of the color hues and thus in a long-lasting iterative process of finding a white color which is to the user""s liking.
It is, inter alia, an object of the invention to provide a white color selection allowing an easy selection of white colors.
To this end, a first aspect of the invention provides a method of selecting a white color temperature of display information. A second aspect of the invention provides a system for selecting a white color temperature of display information. A third aspect of the invention provides a computer which performs such a method. A fourth aspect of the invention provides a monitor incorporating such a system.
The invention is concerned with a white color selection of information to be displayed on a display device of a display apparatus. The invention is particularly relevant for a monitor connected to a computer. The computer supplies video signals to the monitor. A video-processing circuit in the monitor amplifies these video signals to obtain video drive signals supplied to the display device, while a ratio of values (amplitudes) of the drive signals determines the color displayed by the display device.
The invention is based on the recognition that it is far easier to select a white color temperature of the display information if, in the graphical representation of the colors (for example, the color triangle of the prior art), the colors which are defined as white or near-white are graphically indicated. For example, such a graphical indication may be Planck""s curve, or a closed curve surrounding an area of white and near-white colors. The curve may also be formed of separate points or other symbols. It is detected whether the user selects a white color which is on or near the graphical indication of the colors, and only if this condition is met, the values of the drive signals will be corrected in accordance with the correction ratio. The amplitudes of the drive signals determine the amount of light generated by the corresponding primary colors of the display device. In a cathode ray tube, the primary colors are determined by the color points of phosphors, while in a liquid crystal display, the primary colors are determined by color filters. A selected color is on or near the graphical indication if the selected color is on or near Planck""s curve, or if the selected color is on or within the closed curve. xe2x80x9cNearxe2x80x9d should be interpreted as having a distance to the graphical indication in the graphical representation which is less than a predetermined value, or as having coordinates which differ not more than a predetermined value from the color coordinates of the colors represented by the graphical indication.
Plank""s curve as such is known. The white color temperature of a solid surface, for example, a lamp filament or the screen of a cathode ray tube, is the temperature of a so-called black body from which the radiant energy has essentially the same spectral distribution as that of the surface. These white colors are located on the Planck""s curve and are designated with the temperature of the black body resulting in the corresponding white color.
In an embodiment of the invention, a computer comprises a video-generating circuit (often referred to as graphics adapter) and a central processing unit or microprocessor. The graphics adapter supplies the video signals, while the microprocessor controls the graphics adapter to supply the graphical representation and the graphical indication. If the microprocessor detects that a user command indicates a color on or near said graphical indication, the computer sends a correction ratio to the monitor. The monitor comprises a video-processing circuit with the controllable amplifiers, one for each of the video signals supplied by the computer, to supply the video drive signals to the display device. The correction ratio determines a ratio of amplification factors of the controllable amplifiers.
A further embodiment of the invention differs from the above embodiment of the invention in that the computer sends information determining the user-selected color (for example, the x and y chromaticity coordinates) to a calculating circuit in the monitor. This calculating circuit calculates the correction ratio from this information.
An aspect of the invention defines a computer which controls the graphics adapter in such a way that the video signals supplied by the computers are corrected with the correction ratio. For example, the microprocessor calculates corrected values of video information sent to the graphics adapter in accordance with the correction ratio, or the microprocessor supplies the correction ratio to the graphics adapter and the graphics adapter corrects the video information received from the microprocessor.
In an embodiment of the invention, information on the ratios of the drive signals required to display white colors on a specific monitor or monitor type is used to calculate the ratios. In this way, it is possible to accurately reach the white color intended. This becomes increasingly important now that computers are used more and more with applications (for example, photographic applications) in which a true color reproduction is required. The information on the ratios of the drive signals required to display white colors may be provided as software data to be loaded into the computer from a memory. It is also possible to load the software data from the display apparatus via a data interface between the display apparatus and the computer. This data interface may be a separate data bus, or an existing interface which is used also to transport the basic information (the drive signals Ri, Gi, Bi, and synchronization signals) from the computer to the monitor. In the latter case, the data may be encoded on the video or synchronization signals.
In an embodiment of the invention, the information on the ratios consists of a few coefficients only. The coefficients determine a polynomial which represents the drive voltages as a function of the white temperature of the white colors. The computer calculates the required ratios of the drive signals from the functions calculated from the coefficients received.